Comcast promises "100% of advertised speeds, even during peak"
Shared networks can work remarkably well. Across the U.S., AT&T, Comcast, and Verizon are in a fierce marketing battle to offer fiber to new developments. Table stakes now are a reliable gigabit network and premium TV offerings. 400,000 new apartments go up every year. They add less than 1/2 of 1% to the housing stock but are a prime growth market.
I suspect there's a slight exaggeration here, but 97-99% would make most of us very happy. U.S. & U.K. government testing (SamKnows) have long demonstrated that most cable networks are darn close to 100% delivery. In 2014, FCC tests showed 95% of Comcast customers received between 109% and 119% of advertised upload speeds.